The Dana-Farber/Harvard Cancer Center (DF/HCC) Breast Cancer Program seeks to gain a better understanding of breast cancer prevention, risk assessment, epidemiology, genetics and molecular biology, with the hope of translating these findings into meaningful prevention strategies for women at risk of breast cancer and new treatment approaches for those diagnosed with the disease. With the recognition of biologically and clinically distinct breast cancer subtypes, the Breast Cancer Program has increasingly focused on subtypes of the disease. In the next five years, substantive contributions are anticipated in the molecular characterization and treatment of triple-negative disease, HER2+ disease and hormone receptor positive disease. The Program will continue to focus on the development of targeted treatment strategies within molecular subtypes and identify mechanisms of drug resistance. The Breast Cancer Program has been continuously approved by the NCI as an Established Research Program since the inception of the Center. At the time of the last competitive renewal, the Program received outstanding merit. The 110 members span all seven DF/HCC institutions and represent 15 departments of HMS and two departments of HSPH. Members currentiy have $28.7 million in peer-reviewed funding (TC), of which neariy $18 million is from NCI. At the time of the prior competitive renewal, peer-reviewed funding was $16 million, of which $10.1 million was from NCI. This funding total includes several new grants including a V Foundation Award, a Stand Up 2 Cancer award that crosses multiple institutions within and outside of DF/HCC and a Susan G. Komen for the Cure Promise Grant focused on prevention. Program members have published 891 papers during the project period of which 17% were intra-programmatic, 38% were inter-programmatic and 24% were interinstitutional, which reflects a high level of productivity and collaboration. The funding and publication record reflects the broad research base of the Program collaboration among breast cancer researchers.